Abstract : The impact of CO, a by-product of biomass transformation, on the transformation of a model FCC gasolinecomposed of 2-methylthiophene (2MT) and 2,3-dimethylbut-2-ene (23DMB2N) molecules, over MoS2based catalyst supported over alumina was investigated. More specifically, the effect of the presence andthe type of the promoter (Ni or Co) was studied. A gain in activity in HDS of 2MT and hydrogenationof olefins has been confirmed in the presence of the catalysts promoted by cobalt or nickel. However,surpringly, depending on the promoter (Ni or Co), the effect of the presence of CO is really different. Infact, while the carbon monoxide has a significant negative impact on the CoMoS/Al2O3catalyst for thetransformation of model molecules, no effect is observed for other catalysts. These differences could beattributed to a lower adsorption energy of CO on the non-promoted catalyst and promoted by nickelrelative to the catalyst promoted by cobalt as calculated.